This invention relates to printing plates and, more particularly, to the removal of hardened images from printing plates.
A printing plate is prepared for printing by coating an aluminum substrate with a light sensitive film. If the plate is a "negative" plate, the coating hardens when exposed to ultraviolet light; the coating softens for a "positive" plate. The softened areas are then removed by a specific chemical developer, usually an alkaline base product, and the underlying substrate is ink receptive and ready for printing operations.
In some instances, however, there is an error in the image that has been formed on a plate, or it is desired to alter the image for some reason. A new plate might be used to create the new image. but is it desirable to delete the error and correct the image that has been formed so that the entire process does not have to be repeated. It will be appreciated that any image deletion material must completely remove the hardened emulsion in the area to be corrected and to leave the substrate surface prepared for printing. Aluminum plates have an anodized surface that is damaged by some error deletion compounds; some compounds also change the hydrophilic and oleophilic (ink receptive) characteristics of the aluminum plate. Such changes effect the capability of the aluminum plate to produce images of acceptable quality.
There are a number of different imaging processes and plates, e.g., long run plates, fast exposure plates, and laser plates. Also, computer-to-plate (CTP) technology enables a printer to go directly from the copy to an aluminum printing plate. To realize the cost and labor savings of CTP technology, there is a need to delete image errors on the plate in the press. Existing correction solutions do not adequately remove the hardened image material from these plate and do not remove the image in a time compatible with a production environment.
Accordingly, it is an object of the present invention to provide an image deletion solution that is effective to remove hardened images from printing plates without affecting the printing properties of the plates.
Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.